1887.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 441 



The most prominent features by which these four species may be 

 readily distinguished, based, however, solely upon the specimens now 

 in the Xational Museum, are as follows : 



Number of rays, 30 to 40, seldom less than 36 ; rays free for about 

 one-fourth to one-third their length ; spines of upper surface small, 

 very numerous, closely placed, and seldom forming- regular rows ex- 

 cepting along the margins of the rays.— Heliaster microbracliia Xantus 



IS^umber of rays, 35 to 37 (sometimes as few as 24 in the young) ,• rays 

 free for one-fourth to one-third their length ; spines of the upper sur- 

 face, relatively large, subconical in the adult, short and globular in 

 the young, rather widely separated and forming comparatively regular 

 radiating rows outside of the disk. — Heliaster Cumingii Gray. 



Number of rays, 32 to 35 ; rays free for one-half their length or slightly 

 more, sometimes for nearly three-fourths their length ; spines of upijer 

 surface variable in size, small to large, forming regular simple rows 

 along the margins of the rays, and a single, variable medium series, gen- 

 erally not wide. — Heliader heliantlms (Lamk.) Gray. 



Number of rays, 15 to 20, seldom less than 22 ; rays free for more than 

 one-half their length, sometimes for over three-fourths their length 

 stout and well rounded ; spines of upper surface large on disk, and so 

 continuing part way down the median line of the rays ; upper lateral 

 rows of rays regular, simple, consisting of small spines ; median portion 

 of rays occupied by three rows, forming a wide series, in which the in- 

 dividual rows are not always distinct. — Heliaster multiradiata Gray (in- 

 cluding Heliaster Kuhingii Xantus). 



Heliaster microbrachia Xantus. 



Pioc. Phila. Acad., sii, p. 568, 1860. Verrill, Notes on Radiates, in Trans. Conn. 

 Acad. Arts and Sci., i, part 2, 1867-1871, pp. 290, 328, 331, 344, 594. 



This species is readily distinguished by its much more numerous and 

 closely placed abactinal spines, which are uniformly of smaller size 

 than in any other species of the genus excepting H. helianthus, which 

 occasionally agrees with it in this particular ; and by the comparative 

 shortness of the free rays, in which it corresponds only with H. Cum- 

 ingii, of the Galapagos Islands. There are ten specimens* in the collec- 

 tion, all dried preparations, the most of which are in a fair state of pres- 

 ervation. One is the type used by Mr. John Xantus in describing the 

 species; the others have been received from time to time during recent 

 years, and all are from Lower California and the western coast of Mexico. 

 Five of the specimens are below medium size, the others large. The 

 smallest measures about 42'""', the largest 90'"™, in the longest radius. 

 They exhibit comparatively slight variations, although the size, shape, 

 and arrangement of the spines differ somewhat in the different speci- 

 mens. 



" Very many specimens of this specie's have been received since this description was 

 written, but they furnish no additional characters. 



